Large tree mortality and the decline of forest biomass following Amazonian wildfires

Worldwide, forests are increasingly affected by nonnative insects and diseases, some of which cause substantial tree mortality. Forests in the United States have been invaded by a particularly large number (>450) of tree-feeding pest species. While information exists about the ecological impacts of certain pests, region-wide assessments of the composite ecosystem impacts of all species are limited. Here we analyze 92,978 forest plots distributed across the conterminous United States to estimate biomass loss associated with elevated mortality rates caused by the 15 most damaging nonnative forest pests. We find that these species combined caused an additional (i.e., above background levels) tree mortality rate of 5.53 TgC per year. Compensation, in the form of increased growth and recruitment of nonhost species, was not detectable when measured across entire invaded ranges but does occur several decades following pest invasions. In addition, 41.1% of the total live forest biomass in the conterminous United States is at risk of future loss from these 15 pests. These results indicate that forest pest invasions, driven primarily by globalization, represent a huge risk to US forests and have significant impacts on carbon dynamics.

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Twentieth-century shifts in forest structure in California: Denser forests, smaller trees, and increased dominance of oaks

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1410186112 ◽

2015 ◽

Vol 112 (5) ◽

pp. 1458-1463 ◽

Cited By ~ 125

Author(s):

Patrick J. McIntyre ◽

James H. Thorne ◽

Christopher R. Dolanc ◽

Alan L. Flint ◽

Lorraine E. Flint ◽

...

Keyword(s):

Forest Structure ◽

Forest Biomass ◽

Basal Area ◽

Hydrologic Model ◽

Forest Composition ◽

Demographic Shift ◽

Small Tree ◽

Breast Height ◽

Large Tree ◽

Climatic Water Deficit

We document changes in forest structure between historical (1930s) and contemporary (2000s) surveys of California vegetation through comparisons of tree abundance and size across the state and within several ecoregions. Across California, tree density in forested regions increased by 30% between the two time periods, whereas forest biomass in the same regions declined, as indicated by a 19% reduction in basal area. These changes reflect a demographic shift in forest structure: larger trees (>61 cm diameter at breast height) have declined, whereas smaller trees (<30 cm) have increased. Large tree declines were found in all surveyed regions of California, whereas small tree increases were found in every region except the south and central coast. Large tree declines were more severe in areas experiencing greater increases in climatic water deficit since the 1930s, based on a hydrologic model of water balance for historical climates through the 20th century. Forest composition in California in the last century has also shifted toward increased dominance by oaks relative to pines, a pattern consistent with warming and increased water stress, and also with paleohistoric shifts in vegetation in California over the last 150,000 y.

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Understanding the uncertainty in global forest carbon turnover

Biogeosciences ◽

10.5194/bg-17-3961-2020 ◽

2020 ◽

Vol 17 (15) ◽

pp. 3961-3989 ◽

Cited By ~ 1

Author(s):

Thomas A. M. Pugh ◽

Tim Rademacher ◽

Sarah L. Shafer ◽

Jörg Steinkamp ◽

Jonathan Barichivich ◽

...

Keyword(s):

Large Scale ◽

Tree Mortality ◽

Forest Biomass ◽

Turnover Time ◽

Biomass Carbon ◽

Carbon Turnover ◽

Turnover Rates ◽

Wide Range ◽

The Future ◽

Total Turnover

Abstract. The length of time that carbon remains in forest biomass is one of the largest uncertainties in the global carbon cycle, with both recent historical baselines and future responses to environmental change poorly constrained by available observations. In the absence of large-scale observations, models used for global assessments tend to fall back on simplified assumptions of the turnover rates of biomass and soil carbon pools. In this study, the biomass carbon turnover times calculated by an ensemble of contemporary terrestrial biosphere models (TBMs) are analysed to assess their current capability to accurately estimate biomass carbon turnover times in forests and how these times are anticipated to change in the future. Modelled baseline 1985–2014 global average forest biomass turnover times vary from 12.2 to 23.5 years between TBMs. TBM differences in phenological processes, which control allocation to, and turnover rate of, leaves and fine roots, are as important as tree mortality with regard to explaining the variation in total turnover among TBMs. The different governing mechanisms exhibited by each TBM result in a wide range of plausible turnover time projections for the end of the century. Based on these simulations, it is not possible to draw robust conclusions regarding likely future changes in turnover time, and thus biomass change, for different regions. Both spatial and temporal uncertainty in turnover time are strongly linked to model assumptions concerning plant functional type distributions and their controls. Thirteen model-based hypotheses of controls on turnover time are identified, along with recommendations for pragmatic steps to test them using existing and novel observations. Efforts to resolve uncertainty in turnover time, and thus its impacts on the future evolution of biomass carbon stocks across the world's forests, will need to address both mortality and establishment components of forest demography, as well as allocation of carbon to woody versus non-woody biomass growth.

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Global tree-ring analysis reveals rapid decrease in tropical tree longevity with temperature

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2003873117 ◽

2020 ◽

Vol 117 (52) ◽

pp. 33358-33364 ◽

Cited By ~ 1

Author(s):

Giuliano Maselli Locosselli ◽

Roel J. W. Brienen ◽

Melina de Souza Leite ◽

Manuel Gloor ◽

Stefan Krottenthaler ◽

...

Keyword(s):

Tree Ring ◽

Growth Rates ◽

Tree Mortality ◽

Forest Biomass ◽

Global Scale ◽

Forest Composition ◽

Future Evolution ◽

Tree Ring Data ◽

The Tropics ◽

Tropical Lowlands

Forests are the largest terrestrial biomass pool, with over half of this biomass stored in the highly productive tropical lowland forests. The future evolution of forest biomass depends critically on the response of tree longevity and growth rates to future climate. We present an analysis of the variation in tree longevity and growth rate using tree-ring data of 3,343 populations and 438 tree species and assess how climate controls growth and tree longevity across world biomes. Tropical trees grow, on average, two times faster compared to trees from temperate and boreal biomes and live significantly shorter, on average (186 ± 138 y compared to 322 ± 201 y outside the tropics). At the global scale, growth rates and longevity covary strongly with temperature. Within the warm tropical lowlands, where broadleaf species dominate the vegetation, we find consistent decreases in tree longevity with increasing aridity, as well as a pronounced reduction in longevity above mean annual temperatures of 25.4 °C. These independent effects of temperature and water availability on tree longevity in the tropics are consistent with theoretical predictions of increases in evaporative demands at the leaf level under a warmer and drier climate and could explain observed increases in tree mortality in tropical forests, including the Amazon, and shifts in forest composition in western Africa. Our results suggest that conditions supporting only lower tree longevity in the tropical lowlands are likely to expand under future drier and especially warmer climates.

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The importance of history in understanding large tree mortality in African savannas

Ecography ◽

10.1111/ecog.06012 ◽

2021 ◽

Author(s):

Arundhati A. Das ◽

Maria Thaker ◽

Corli Coetsee ◽

Rob Slotow ◽

Abi T. Vanak

Keyword(s):

Tree Mortality ◽

Large Tree

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Tracking tree mortality across sites with repeat LiDAR data

10.5194/egusphere-egu21-4365 ◽

2021 ◽

Author(s):

Toby Jackson ◽

Matheus Nunes ◽

Grégoire Vincent ◽

David Coomes

Keyword(s):

Forest Structure ◽

Tree Mortality ◽

Mortality Rates ◽

Landscape Scale ◽

Airborne Lidar ◽

Lidar Data ◽

Forest Types ◽

Large Tree ◽

Airborne Lidar Data ◽

Field Plots

<p>Repeat airborne LiDAR data provides a unique opportunity to study tree mortality at the landscape scale. We use maps of canopy height derived from repeat LiDAR (two or more scans collected a few years apart) to detect changes in forest structure. Visually, the most obvious changes are caused by large treefall events, which are difficult to study using field plots due to their rarity. While repeat LiDAR data provides exciting new possibilities, validation is a challenge, since we cannot easily determine how many trees have died and we may miss trees which are dead but still standing. I will discuss our progress so far, studying large-tree mortality rates across multiple countries and forest types.</p>

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Hybrid Rootstocks for Valencia Sweet Orange in Rainfed Cultivation Under Tropical Savannah Climate

Journal of Agricultural Science ◽

10.5539/jas.v12n11p40 ◽

2020 ◽

Vol 12 (11) ◽

pp. 40

Author(s):

Danilo Pereira Costa ◽

Eduardo Sanches Stuchi ◽

Eduardo Augusto Girardi ◽

Abelmon da Silva Gesteira ◽

Maurício Antonio Coelho Filho ◽

...

Keyword(s):

Drought Tolerance ◽

Production Efficiency ◽

Tree Mortality ◽

Sweet Orange ◽

Fruit Production ◽

Tree Size ◽

Soluble Solids ◽

High Yield ◽

Rangpur Lime ◽

Large Tree

The performance of Valencia sweet orange grafted onto 41 hybrid citrus rootstocks was evaluated for 11 years in rainfed cultivation under tropical savannah climate (Aw type) in Brazil, in addition to three selections of the standard drought-tolerant Rangpur lime and two selections of Sunki mandarin. Drought tolerance, assessed by visual score of leaf wilting, was directly related to the mean fruit yield. Indio and Riverside citrandarins, Tropical Sunki mandarin and the hybrid TSKC × CTSW-028 were grouped with the most productive selections of Rangpur lime, all of them inducing large tree size, intermediate fruit production efficiency, and high drought tolerance. The hybrid TSK × TR English-CO was similar except by inducing a higher mean soluble solids concentration in the orange juice. A third group of rootstocks induced high yield and drought tolerance, and a mean 30% reduction in tree size that led to high production efficiency, which comprised the hybrids HTR-053, TSKC × (LCR × TR)-017 and-059, TSKC × CTSW-041, LCR × TR-001 and San Diego citrandarin. The tree mortality on Rangpur lime selections was as least as 46%, while more than 80% of trees grafted onto the aforementioned rootstocks survived without visual symptoms of citrus sudden death disease or graft incompatibility. The selected hybrids and Tropical Sunki mandarin also induced fruit quality, mainly soluble solids, superior to the Rangpur lime and, therefore, are potential rootstocks for rainfed cultivation of Valencia sweet orange.

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Understanding the uncertainty in global forest carbon turnover

10.5194/bg-2019-491 ◽

2020 ◽

Author(s):

Thomas A. M. Pugh ◽

Tim T. Rademacher ◽

Sarah L. Shafer ◽

Jörg Steinkamp ◽

Jonathan Barichivich ◽

...

Keyword(s):

Large Scale ◽

Tree Mortality ◽

Forest Biomass ◽

Turnover Time ◽

Biomass Carbon ◽

Carbon Turnover ◽

Turnover Rates ◽

Temporal Uncertainty ◽

Wide Range ◽

Total Turnover

Abstract. The length of time that carbon remains in forest biomass is one of the largest uncertainties in the global carbon cycle, with both recent-historical baselines and future responses to environmental change poorly constrained by available observations. In the absence of large-scale observations, models tend to fall back on simplified assumptions of the turnover rates of biomass and soil carbon pools to make global assessments. In this study, the biomass carbon turnover times calculated by an ensemble of contemporary terrestrial biosphere models (TBMs) are analysed to assess their current capability to accurately estimate biomass carbon turnover times in forests and how these times are anticipated to change in the future. Modelled baseline 1985–2014 global forest biomass turnover times vary from 12.2 to 23.5 years between models. TBM differences in phenological processes, which control allocation to and turnover rate of leaves and fine roots, are as important as tree mortality with regard to explaining the variation in total turnover among TBMs. The different governing mechanisms exhibited by each TBM result in a wide range of plausible turnover time projections for the end of the century. Based on these simulations, it is not possible to draw robust conclusions regarding likely future changes in turnover time for different regions. Both spatial and temporal uncertainty in turnover time are strongly linked to model assumptions concerning plant functional type distributions and their controls. Twelve model-based hypotheses are identified, along with recommendations for pragmatic steps to test them using existing and novel observations, which would help to reduce both spatial and temporal uncertainty in turnover time. Efforts to resolve uncertainty in turnover time will need to address both mortality and establishment components of forest demography, as well as key drivers of demography such as allocation of carbon to woody versus non-woody biomass growth.

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